Forget all those debates about background checks and gun show loopholes, because now it is very easy and completely legal to make a firearm right in the comfort of your own home. We are talking high-powered rifles that are totally untraceable. Tonight the results of a joint investigation by our partners at fusion and univision. Here is fusion's chief investigative reporter Maryann vanzeller. This is it. One in the chamber. Aim at the center dot. And take a shot. Have fun. &#9834; There you go. Reporter: This morning this gun didn't exist. Just a pile of metal parts. But now -- definitely works. This ar-15 was built from a kit you can buy online. It can shoot 4 around a minute. It has no record of sale and no serial number. The government has no clue it exists. And that's just how he wants it. What our goal was is to get as many of these on to the streets as humanly possible and, and, my opinion, an armed society is a just society. Reporter: In Oceanside, California, Dimitri made a big business out of selling kits easily turned into guns. Because of the way the gun law works no background check is required. Everything that is shipped from our company, ordered through the website comes through the building and goes out. You have Texas, Connecticut, Michigan. Reporter: You can legally build a gun as long as you don't sell it or give it away. Easier than assembling an IKEA dresser. So would I be able to do this if I wanted to? You would be. Reporter: Legally I could do this if I wanted to? Absolutely. As long as you are able to own a firearm, not restricted from firearm ownership. If you are restricted from owning a firearm making one would be illegal. Reporter: But our reporting shows that weapons like the one we shot are going to criminals. They're arming gang members in L.A. Gang members that have terrorized this community. Reporter: Cartels in Mexico. Reporter: Even a mass murderer. Requesting assistance on shooter, multiple victims down. Reporter: Last June in Santa Monica, John zawari killed six people with this weapon. He fried tried to buy a gun, bought the pieces on line and built his own assault rifle. The same day sandy hook happened in China there was a massive, knife massacre occur. Should we go out and say knives are the problem in China, force people to go through background checks to have knives. Reporter: While he sells everything you need to make a gun at his shop heap is not a firearms dealer and he says he doesn't need to be. It ooelts either is a firearm or not a firearm. A black and white situation. These are not firearms. Not one single firearm here? No. Not for sale. It all goes back to the gun control act of 1968 which defines what a firearm is. A rifle, as far as the government is concerned is this. Called ail receiver which connects the mechanical part and makes the gun go boom. Receivers are regulated and stamped with serial Numbers and registered with the fed the you need to pass a background check to buy one unless you buy one that is not quite finished. One that need a couple more holes drilled in it. That's called an unfinished or 80% receiver. And the law says, it's not a gun. This is basically what is called an 80% lower receiver. And this is considered a gun. This is a gun. This is not. It takes about 45 minutes at a drill press to do the job. If you don't have one of those, there is now an even easier way. Plastic receivers that can be finished with a $50 tool. Really, really cool. These ones the experience level is lower. You can build that at home. You see this, the job is all done for you right here. You can see this is another color, black, so you know where you need how to cut it. And you have the little parts here. That also demonstrate where you need to cut it. Di he will sell 75,000 unfinished receivers this year mostly on line. No background check necessary. Meaning anybody can buy one. Who is there to know if I am allowed to buy this gun or not. Essentially making a gun. Nobody knows if I am allowed. You as a responsible American citizen should know whether you are allowed to own a firearm or not. Not one of those, IFS, ands, but buts. This way is more complicated than to buy them on the street out of the trunk or go through whatever illegal activity they go through to get the weapon. Reporter: The ATF says the guns are increasingly popping up at crime scenes. What is this? This is an ar-15. Home made from -- from an unfinished lower receiver. And this weapon was purchased by ATF undercover agent from gang members here in, in Los Angeles. This is a completely untraceable firearm. How challenging does it make your job? Extremely challenging. They teach ATF agents. They've tell us. Every gun tells a story. This gun does not talk. This gun is mute. Reporter: So turning its attention to the trade in unfinished receivers. If somebody is making this into this -- my job is to try to stop that. Reporter: Last year the ATF raided the gun part stores across California. Twul men were charge twul -- two men were charged. The ATF confiscated 345 guns. Are you afraid the government will stop you guys from selling these receivers? And from building your own guns? No, I am not afraid of the government at all. In fact the government should be afraid of the people not the other way around. Reporter: In March, just two weeks after we interviewed him, the ATF raided Dimitri's stores. He says they seized 6,000 unfinished plastic receivers just like the one he's showed us. Dimitri told us the government kids the plastic ones too close to being a finished receiver but he is still in business and he believes he has already succeeded. I am willing to bet there is hundred of thousand if not millions of the receivers that are ak shaefl actually in the country. One of the things they can pass the laws they want. These things are out there. Reporter: You think in that way you have sort of done -- done your job. I am somewhat proud of the accomplishment, yes, yes, yes. That is something I will put it on my gravestone. It its part to arm the people. And the defendant's charged with illegally making and

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